I have an 08 Impreza 2.5i 5 door automatic, approx 20,000 miles.

Today when I tried to start the car the starter would not stay engaged.  
When I turned the key it would crank for a second or two and then stopped
cranking. This happened several times before I was finally able to get the
car started.  When I went to start the car again later in the day it
started just fine.

There was no sign that the battery was weak. Today was moderatly cold and
snowy but nothing ususual.

I don't know if this is a one time occurance, but I know things that happen
once tend to happen again, and usually at the most inoportune time.  And
the car is still on warranty, but I wonder if it doesn't happen again is
there any point in bringing it in and having them look at it.

Has this happened to anyone else, and what was the outcome?